Push-to-connect fittings are well known and used in a wide-variety of pneumatic, hydraulic, and other fluid transport applications because of their ability to quickly connect and disconnect tubular elements. In automotive applications, push-to-connect fittings are frequently used to connect various sections of tubing in air suspension systems, braking systems, and transmissions. The Department of Transportation (DOT) and Society of Automotive Engineers (SAE) have implemented various standards for such fittings. For example, pull tests for the fittings include withstanding 150 lbs of force for a ⅜″ tube fitting and 200 lbs of force for a ½″ fitting in both ambient temperature and boiling water. Low temperature impact testing requires the fitting to withstand a one pound weight being dropped on a nose of the fitting at −40° F. To meet these standards, previous push-to-connect fitting designs have utilized barbs that are pushed into the smooth bore of a plastic body of the fitting. However, barbs have a tendency to migrate when being pulled, and thus, certain designs place a metal ring on the outside diameter of the fitting to prevent the plastic body from expanding and allowing the barbed piece from becoming disconnected from the plastic body. The use of such metal rings increases material and manufacturing costs, which is undesirable in an industrial environment.
In addition, previous designs have also utilized plastic ends to connect the tubular elements to the body of the fitting. These plastic ends are susceptible to shattering or cracking, which is also undesirable in an industrial environment.
Therefore, it is desirable to have a coupling apparatus that is DOT and SAE compliant (i.e., will withstand the appropriate force levels during pull testing and will not shatter during low temperature impact testing), while weighing less and costing less to manufacture than conventional push-to-connect fittings.